Piston



Sept., lo, 1929.

N. A. BEST ET AL PIvsToN Filed April 2l, 1925 INVENTORS` Norman A. Best By John E.Hoy

ATTORN S.

ton are small, is well recognized (see article satema sept. ie, i929.

UNITED STATES NORMAN A. Bns'r AND JOHN n now CHEMICAL COMPANY, or GAN.

` ramen PATENT ,oFFlCE HOvY, 0F MIDLAND, MICHIGAN, ASSIGNORS 'TO THE MIDLAND, MICHIGAN, A CORPORATION 0F MICHI- .application exea Aprn 21, 1925. serial No. 2435i entitled Scuied pistons result from cold jacket and lack of oil by Frank Jardine in Automotive Industries, issue of July 31,

1924:). In other words, while a `relatively small quantity of oil is suflicient for lubrication at the point in question when the engine -is at normal running temperature, when cooled to lower temperature, as when left standing in cold weather, the provision ordivwalls has been found entirely inadequate:

The present invention has as one principal object the inclusion in a piston of so-called composite type of means whereby lubricant in adequate amount is immediately suppliedto i andb related ends,

the bearing surface of the surrounding cylinder even when the engine is started cold. More particularly, the invention relates to a novel form of composite piston in which the l 25 head and -body Vthereof isl cast of light metal with a'shell of iron or steel surrounding and attached to the skirt portion. It will be understood, however, that the principle of the invention is not limited to such particular type, of piston.

'To the accomplishment of the foregoing the invention, then, consists ofthe means hereinafter fully described and particularly pointed out in the claims,

' the annexed drawing and the following description setting forth in detail certain mechanism embodying` the invention, such disclosed means constituting, however, but one of various mechanical forms in which the principle of the invention may be used. In said annexed drawingz-jj- Fig. 1 is partly a side elevation and partly a central vertical ing' the present improvements; Fig. 2 is a central vertical section thereof taken on a plane at right angle?l to the plane of -the sectioned portion of l.; andlfig. 3 is a sectional view on the same plane as that of Fig. 2.. but showing apart from the main body of the piston a shell or sleeve that constitutes made for. lubricating such cylinder section of a pistonembody-l the wearing portion of the skirt of said piston In its general features of Construction the illustrated pistonl is similar-to those of cast iron or light metal alloys heretofore used in internal combustion engines. In other words, such piston comprises a more' or less, cylindrical head portion 1 fron which depends a sleeve or skirt portion 2. The latter vis formed with oppositely placed, inwardly directed bosses 3 which are apertured'to receive awrist pin (not shown),

bronze or equivalent bearing metal are preferably fitted to the aperturesin suelrbosses, as best shown in Fig. l, and an integral rib 5 between each boss and the head 1 contributes whereby-the piston is-a t- Y l tached to the connecting rod. Bushings 4 of.

to the strength of the structure. In order effectually to seal the piston within the walls of the cylinder within which it works, resilient piston, rings l(not shown) of familiar construction are seated in annular recesses 6 Vin-head portion, as need not be further ex-r plained.

As hereinbefore indicated, the main'body of the pistoncomprising 'such head portion 1 and skirt 2 will preferably be cast of a light metal alloy as for example one of the known aluminum or magnesium alloys. available for this purpose. Substantially surrounding such skirt portion-2 is a shell or band 7 which, in contradistinction to the light metal alloy whereof the piston proper is composed, will be made either of Cast ironvor steel or other metal having a relatively low coeliicient of expansion. Cast iron will be preferably used for'such shell or expansion will be the sam'e,v or approximately the same, as the walls of the engine cylinder which is ordinarily made of cast iron.

Where such shell, as illustrated in the ligures of the drawing, extends above the wrist pin openings in bosses 3, it will be formed with corresponding openings 8, somewhat larger diameter, and the lower edge 'of such shell will furthermore terminatev somewhat short of the lower edge of the piston skirt-2. Adjacent its upper and lower edges, as well as at an intermediate point lyingA approimately midway between such preferably of' i has been previously placed,'the walls of the mold being formed to give the proper contour lto the exposed portions of the body and skirt.

' Accordingly, at the temperature of casting, the skirt portion 2 and such shell Twill be in close fitting contact throughout and this condition will be approximated at the relatively high temperature obtaining nwithin the engine cylinder under normal operatingconditions. However, whenthe engine is cold and the temperature of the piston accordingly much reduced below such normal operating temperature, the skirt being made, as indicated, of metal having a lower coeiiicient of expansion than the shell will contract a correspondingly greater amount and a space will be left not only between the inner edges of the 'ribs 9, 10 and l1 and the bottoms of the corresponding grooves 12, 13 and 14s, but also between the cylindrical opposed faces of the skirt and shell that ,lic between said ribs. l

It willy be noted, as best shown in Fig. 3,

l that the lateral surfaces of said ribs 9, 10 and U11 and the corresponding contacting surfaces.

of the respective grooves 12, 13 and 14, are inclined more or less with respect to the cylindrical face of the body, the lines a of contact in the particular construction shown being such as to meet at a point Z; on the central axial line within the piston. This pointer other corresponding point thus selected within the piston may be referred to as the neutral expansion point of the structure and, as signifled'by this term, the result of havingthe lateral engaging'surfaces of the parts in question thus all diverge from .Such common central point within the piston will be to maintain` such surfaces in contact, irrespective of any changes in the piston skirt and surrounding shell due to their contraction or expansin, this ldespite the differences in the rate of such contraction or expansion occasioned by the dierence in the coefhcients of expansion of the metals whereof the parts in question are res ectively formed.

ccordingly, the shell or band 7 will at all times remain firmly attached to the piston skirt 2 through the medium of ribs 9, 10 and 11, it being understood that projections of other forms may be utilized in the manner j ust described in place of such ribs specifically. The foregoing construction, however, will not prevent the separation to a slight degree in the manner hereinbefore explained of the cylindrical faces of the shirt and such shell, it being noted that they are shown as avancee thus separated in Figs. 1 and 2 which therefore `represent the piston before it has become heated up in operation. However, the annular spaces 15 just referred to are measurably decreased in capacity, immediately the piston becomes heated, and such capacity will thenagain increase when the piston again cools off. I

The shell 7 is provided `with a series of holes 16 that are drilled or otherwise formed therein so as to provide for the flow of the oil or other lubricant ordinarily-used in internal combustion engines between the spaces in question and the outer surface of the shell. It will be understood that the location of these holes will vary to suit different conditions of service as well as different designs of piston. When the engine is running, `the spaces although reduced to minimum capacity, will tend to fill up with oil that is drawn in through such openings 15 and when the en-Y gine is stopped and cools off, due to the increase in capacity of such spaces, more oil will be drawn in from the lclearance space surrounding the gliding surface of the piston. ,If desired, a shallow groove 17, as shown in association with the lower circle of openings V16, may be provided in the outer cylindrical surface of the shell 7 to insure a suiiicient supply of oil thus to fill the corresponding space 15. When the engine'is again star'ted up, the body of the piston, due to its greater coetlicient of expansion and to the fact that the head of the piston is of course directly exposed to the heat of gases of combustion in the explosion chamber of the engine, begins to expand immediately and more rapidly than the shell. rlhe excess oil in the spaces 15 is accordingly forced out, thus lubricating the gliding surface of the piston, irrespective of whether the means, e. g. splash system or the like provided for such lubrication, beginto function properly at once kor not. Even where oil is not actually forced out from recesses 15, due to there having been an insuliicient quantity' available to fill such spaces, contraction of these spaces will raise the oil therein high enough to cause it to iiow out through the holes 16 .by gravity.

The spaces in question, it will accordingly be seen, constitute in effect an oil reservoir in the piston itself which automatically op crates to take up and .discharge oil under conditions when the ordinary lubricating means provided in internal combustion engines are ineffective, if not entirely inoperative. In

,other words, the piston is insured of suicien't iis We therefore particularly point out and distinctly claim as our invention l. A piston7 or like mechanical element74 formed with an encircling reservoir for supplying lubricant-to the bearing surface, the

inner and outer walls boundingv such reser- 'voir being formed of metals having differhaving openings adapted to provide coininunication between such reservoir and thc gliding surface of the piston. y

3.' In a piston, or like mechanical element,

the combination of a body and a part sur rounding the same, said body and part being composed of metals having ditferent coveiiicients of expansion and beingl formed to provide an interposed annular space of vari able capacity depending upon temperature and communicating with the gliding surface of the piston. l Y

4:. In a piston, or like mechanical element, the combination of a body and a part surrounding the same, said body and part be; ing formed to provide an interposed annular space for supply of lubricant to the gliding surface, and said body beingY composed of a metal having a higher co-eiiicient of expansion than said surrounding part, whereby the capacity of such space is increased upon fall, and decreased upon rise of temperature.

5. In a piston, or like mechanical element, the combination of a body composed of a light metal alloy, and a shell of ferrous metal surrounding said body, said body and shell being formed to provide an interposed annular space that is closed save for openings in said shell adapted to provide communication between such space and the gliding surface of the piston.

6. In a piston, or like mechanical element, the combination of a body composed of a light metal alloy, and a shell of ferrous metal to provide communication between such space and the gliding surface of the piston 'i '7. ln a piston, 'or like mechanical element,

the combination of a body composed of a light inet-al alloy, and a shell of ferrous metal surrounding said body, said body and shell being formed to provide a plurality of interposed annular spaces and said shell having corresponding encircling series of openings adapted to provide communication between such spaces, 1respectively7 and the gliding surface of the piston.

8. In a piston, or like mechanical element, the combination of a body composed of a light metal alloy, and a shell of ferrous metal surrounding said body, said body and shell being formed with inter-engaging ribs and grooves whereby an interposed annular space is provided, and said shell having openings adapted to provide communication :between such space and the gliding surface of the piston.

Signed by us, this 17th day of April, 1925.

. JOHN E. HOY.

NORMAN A. BEST. 

